The Internet is gaining increasingly in importance as a data network. Both the number of subscribers and the amounts of data transmitted by each subscriber are constantly increasing. For private subscribers in particular, access to the data network, which usually takes place via the conventional telephone network, proves to be a critical bottleneck. Traditional access techniques restrict the data rate, since the telephone network was originally optimized for voice communication.
Therefore, the XDSL transmission system was developed for rapid Internet access. FIG. 1 shows an XDSL data transmission system according to the prior art. The XDSL data transmission system uses the existing twin copper wires of the conventional telephone network. In this case, the subscribers are connected by means of an XDSL modem to a central exchange via an associated two-wire telephone line in each case. The central exchange is connected to the data network, for example the Internet, and the conventional telephone network. The voice and data signals are bidirectionally transmitted between the central exchange and the subscriber XDSL modem via the two-wire telephone lines. The disadvantage of the telecommunication system represented in FIG. 1 is that the range between the exchange and the subscriber modems is very limited and the costs for providing the infrastructure are very high. Each subscriber must have an XDSL modem of its own for the connection of the PC and the telephone. In addition, a corresponding XDSL modem must likewise be provided in the central exchange for each subscriber. The expenditure on circuitry for such a telecommunication system is therefore very high. In addition, it is not possible for many end subscribers to be connected to the XDSL telecommunication system, since the distance between the central exchange and the private household is too great.
For such private households, the prior-art telecommunication system represented in FIG. 2 was therefore proposed. In the case of the telecommunication system represented in FIG. 2, the end subscribers are connected via a 10 Base S modem to a local 10 Base S switch. U.S. Pat. No. 6,088,368 describes the circuitry of the 10 Base S modem in detail. The 10 Base S telecommunication system described there is capable of transmitting about 10 megabits per second of data via a conventional copper infrastructure. The 10 Base S telecommunication system uses carrierless amplitude and phase modulation. A specific choice of the carrier frequency prevents the need for the carrier frequency itself to be transmitted here. A special form of 64 quadrature amplitude modulation is involved. With the 10 Base S data transmission system, it is possible to achieve a very high data transmission rate via the conventional twisted copper telephone lines, which were originally designed with bandwidths between 300 kHz and 400 kHz for voice signal transmission. The 10 Base S switching device is connected via local two-wire telephone lines to the respective 10 Base S modem of the end subscribers. A data processing terminal or PC and a voice signal terminal or telephone are respectively connected to the 10 Base S modems. The 10 Base S switch is connected via a local data transmission network, for example an Ethernet network, to a BWA modem (BWA: Broadband Wireless Access). The BWA modem is connected to an antenna for the bidirectional data exchange via a radio link. A radio link serves for the bidirectional data exchange between the local antenna and a central antenna, which is connected to a data network, for example the Internet. The disadvantage of the telecommunication system for the bidirectional transmission of data and voice signals represented in FIG. 2 is that the data transmission link is very susceptible to disturbances. In addition, many buildings with local antennas cannot exchange a data signal with the central antenna on account of shadows or obstacles. The expenditure on circuitry for the infrastructure represented in FIG. 2 is likewise high, since a relatively large number of antennas have to be provided to provide coverage for all the buildings to exchange data with the data network.
The telecommunication system for the bidirectional transmission of data and voice signals represented in FIG. 3 was therefore proposed. FIG. 3 shows a telecommunication system which on the one hand uses a 2-way satellite system with a cable network for the data transmission to the building and in the building and on the other hand comprises a conventional telephone system for the voice transmission to the building and in the building. The 2-way system is described in detail in the standard ETSI TR 101 790. A data network in this case exchanges data via a gateway and via a central satellite system with a satellite, which serves as a relay station. The data transmitted to the satellite are transmitted from the latter to a local satellite device. This satellite device comprises an outdoor satellite unit (ODU: Outdoor Unit) and an indoor satellite unit (IDU: Indoor Unit). The indoor satellite unit is connected via a cable head end and a coax cable network to a multiplicity of subscriber data modems in the private households. Respectively connected to the subscriber data modems is a data processing terminal, for example a PC. The subscriber terminals transmit data via via the coax cable network, the local satellite device and the satellite transmission link to the central satellite system, which is connected to the data network. Each subscriber additionally has a conventional telephone, which is connected via further telephone line to a central exchange. The central exchange is connected to the conventional telephone network. In the case of the conventional telecommunication system represented in FIG. 3, the bidirectional voice signal transmission and the bidirectional data transmission take place in two separate telecommunication systems. The disadvantage of the telecommunication system for the bidirectional transmission of data and voice signals represented in FIG. 3 is that an independent cable network has to be provided in each case for the data transmission. The setting up of such an infrastructure, for example a coax cable network to provide the data link for all the end subscribers, is very complex and costly.